I get an error.

What's the error?

The example code you've posted is not complete, won't work as posted. I made a few changes to get it to run, and it runs without errors.

The difference between ($x) = (f()) and $x = f(), in a nutshell, is that the first one puts the function in a list context. In the second example, the function is called in a scalar context.

Without more of your code, I don't know what's going on.